The present invention relates generally to hand operated routers and more particulary to routers of the plunge type in which the driving motor and associated cutting bit are reciprocably movable with respect to the workpiece engaging base housing.
Plunge type routers are similar to conventional routers in that they include a driving motor having a bit holding chuck secured to one end of the motor drive shaft which motor is axially movably supported within a base housing. However, while in conventional non-plunge type routers, the motor is locked in position relative to the base housing such that the cutting tool or bit projects axially outwardly from the workpiece engaging surface of the base housing to the desired depth of cut at all times, the plunge type routers provide biasing means which operate to retract the cutting tool or bit into the base housing during periods of non-use.
Typically, such plunge type routers have required completely differently designed motor and base housings from those used in conjunction with non-plunge type routers in order to accommodate return biasing and guide means. In one form, the drivimg motor is movably supported on a base member by a pair of generally cylindrical support posts extending upwardly from the base member and telescopically received within a portion of the motor housing. Typically, the support posts are of a hollow construction and suitable compression springs are mounted therein which operate to bias the motor and associated cutting bit into a retracted position. While this biasing and support arrangment may initially offer satisfactory performance, it is relatively expensive to manufacture due to the need to adhere to relatively close tolerances between the telescoping support posts so as to provide a smooth movement thereof while the biasing spring is being compressed. Further, because such constructions have the biasing springs compressibly positioned within normally two relatively small diameter support posts having limited engaging surface area, both the support posts and biasing springs are subject to wear resulting from the continuous reciprocating compression and relaxation movement of the biasing spring during operation of the router. This resulting wear may result in premature breakage or weakening of the biasing springs or may allow excessive lateral movement of the motor relative to the base resulting in cocking or other objectionable movement of the cutting tool during a plunge operation or may cause the motor to "hang up", any one of which may result in erroneous cuts in the workpiece.
The present invention, however, overcomes these disadvantages by employing a pair of extension springs extending between projections formed on a base housing of a design similar to that of non-plunge type routers which base housing also includes an upstanding generally cylindrically shaped portion having a bore extending therethrough within which the motor assembly is movably supported and guided. A pair of projections are also secured to the lower end of the motor housing and a pair of springs are connected between the motor assembly projections and the base housing projections which operate to bias the motor assembly into a retracted position. Suitable handles are also provided which are secured to the motor housing so as to overlie and protect the extension springs.
Thus, the present invention provides an economical plunge type router construction which not only substantially reduces the cost of manufacturing by eliminating the need for closely machined telescopic support posts but also provides improved reliability of operation by significantly reducing wear because the biasing springs are located remotely from the movement guiding means. Reliability of the router is also enhanced because the wear resulting from reciprocable movement of the motor assembly is spread around the entire circumference of the motor housing.
Further, the construction of the present invention allows a standard motor housing to be used in construction of both plunge and non-plunge type routers thereby offering additional manufacturing cost savings. It should also be noted that because the biasing springs are readily accessible by merely removing the handles, replacement thereof may be very easily and quickly accomplished thus reducing the time during which the tool is out of service.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.